1. Field of the Invention
The present invention relates to a system for evaluating ease-of-use (usability) of a human interface device, such as a control panel of a machine and a plant and an input and output device of a computer, by computer simulation. In particular, the present invention relates to a system for evaluating usability which is suitably used to design an easy-to-use human interface device, and a system and a method for evaluating usability of a human interface device by simulation.
2. Description of the Related Art
To design a human interface of a system that interacts with an operator using various types of inputs and outputs and to evaluate usability of the interface, one of the following known methods has been employed, depending on the function and usability: (1) A method for designing improved operation of individual elements; (2) A method for designing improved operation adaptable to operator's intuition; (3) A method for designing improved operation by differentiating similar elements; (4) A method for designing improved operation by aggregation of operation tasks; (5) A usability evaluation method using operators; (6) A usability evaluation method using a digital mannequin; (7) An operator-workload evaluation method using operation schedule simulation.
(1) Method for Designing Improved Operation of Individual Elements
This method, in a design phase, is characterized in that each human interface element, such as a control panel element including a button and a lever, and a visual screen element on a screen is designed to avoid human perceptional and operational errors. In an evaluation phase, the amount and qualities of features of the elements are evaluated for every element and are added. The total value is used for the usability evaluation of the entire system. For example, a button considered to be frequently used during normal operation is enlarged and painted with a striking color, as is disclosed in “Ergonomics—Office work with visual display terminals (VDTs)—Menu dialogues”, JIS Z 8524:1999, Identical translation of ISO 9241-14, 8.1.6a, 1997.
(2) Method for Designing Improved Operation Adaptable to Operator's Intuition
According to this method, in the design phase, features of human interface elements are designed so as to adapt to human psychological characteristics. In the evaluation phase, the adaptation rates of the feature of each human interface element are measured and added for the entire system to evaluate the usability. For example, a moving machine is moved forward by forcing a lever forward. Since the moving direction of the machine is identical to the tilting direction of the lever, the operator intuitively and easily memorizes the operation, as is disclosed in “Introduction to Ergonomics”, by R. S. Bridger, McGraw-Hill, Inc., 1995.
(3) Method for Designing Improved Operation by Differentiating Similar Elements
According to this method, features of human interface elements having similar display positions, display sequences, and perceptual properties are designed to decrease the similarity, and therefore, the recognition error between similar elements is reduced. In the evaluation phase, the usability is evaluated by a small similarity between the interface elements. For example, by disposing small protrusions on the “F” and “J” keys on a keyboard, these keys are distinguishable from the adjacent keys, and therefore, the recognition error is suppressed during touch typing.
(4) Method for Designing Improved Operation by Aggregation of Operation Tasks
According to this method, a typical operational activity sequence of an operator is defined, and one unit of operational activity is evaluated in consideration with the previous operational activity. In a design phase, the previous operational activity is determined to suppress recognition errors and operational errors in the unit of activity. For example, when an operator of a control panel of a plant performs an operation in a typical turn (step), buttons to be depressed for the steps are arranged in a line from left to right in the depressing order. Thus, the recognition error of the buttons and sequence error of depressing the buttons are suppressed, as is disclosed in “Human Error Evaluation Methods for Fieldworks”, by Satoko Sakajo, Takashi Nakagawa, and Naotaka Terashita, Proceedings of the Sensing Forum of The Society of Instrument and Control Engineers, pp. 65-69, 2002 (in Japanese).
(5) Usability Evaluation Method Using Operators
According to this method, operators actually operate an object to be evaluated, and the operation activity is then analyzed. In addition, subjective opinions of the experimental subjects are taken to evaluate the usability of the object.
(6) Usability Evaluation Method Using a Digital Mannequin
According to this method, by using an operation object model and a digital mannequin, which are created by modeling the shape of an operation object and the human body mechanism of an operator, respectively, operation activities are simulated, and then the usability of the operation object is evaluated.
(7) Operator-Workload Evaluation Method Using Operation Schedule Simulation.
According to this method, a scenario of an operation schedule for control of a specific plant is prepared, and a simulation that estimates the workload which an operator feels is executed by a computer to estimate an operating state and the operator's workload in that state. By this simulation, the usability of the operation object is evaluated. For example, a “man-machine interface design evaluating device” is disclosed in Japanese Unexamined Patent Application Publication No. 9-258817.
This man-machine interface design evaluating device evaluates man-machine interface design, such as a control panel of a plant and a CRT screen, in terms of functionality and usability. To evaluate the man-machine interface design for monitoring a plant operation, this device includes an input and display unit that communicates with an operator, a design data editing unit that creates or edits man-machine interface design data based on the information via the input and display unit, a design database that stores the design data created by the design data editing unit, a plant simulation unit that simulates any operating state of the plant, a man-machine interface simulation unit that simulates displayed information of the man-machine interface based on plant data from the plant simulation unit and the design data from design database and that displays an operating state of the man-machine interface on the input and display unit, a human activity simulation unit that simulates a human activity which sends and receive data to and from the simulated man-machine interface, and a human activity evaluation unit that evaluates human activity data simulated by the human activity simulation unit.
However, the methods described in (1) and (2) above are used to qualitatively evaluate an individual human interface element so as to improve and design it, and therefore, these methods do not provide satisfactory guidelines to increase ease-of-usability through the entire human interface structure.
The method described in (3) above is used to qualitatively suppress the confusion of an individual human interface element with a similar one, and therefore, this method does not provide satisfactory guidelines to improve ease-of-usability through the entire human interface structure. Moreover, in actual usage environments, estimating the effect on suppression of the confusion is difficult.
The method described in (4) above is used to design and evaluate usability only for an operation sequence of a specifically assumed task, not for an operation sequence in actual usage environments. In particular, even in a typical operation activity sequence, interruption or sequence change sometimes occurs during execution. Therefore, the assumption used in the evaluation of the operation activity is not always true, which is a problem.
In the method described in (5) above, to obtain a sufficiently effective usability evaluation result, experiments using a large number of operators are required. This increases the cost due to the time and materials required, thus limiting the number of types of objects to be evaluated and the number of experimental items. Also, even the property of a single operator varies with the experience and fatigue of the operator. Consequently, a comparison between a long-term experimental result and a short-term experimental result is difficult, which is a problem.
In the method described in (6) above, since a kinetic interaction between an evaluation object and a digital mannequin is simulated, the evaluation is only focused on kinetic usability items, such as workload caused by a gravitational force and energy consumption. Consequently, the usability in terms of perception, recognition, and judgment of the operation is not directly evaluated, which is a problem.
In particular, a trial has not been done in which perception information to be perceived by the digital mannequin is simulated sufficiently accurately in accordance with simulation environment, and in which the digital mannequin carries out an action based on the perception information. Therefore, although human passive activities can be simulated, the simulation of human active activities is difficult.
Furthermore, in this method, since no perception information to be perceived by the digital mannequin is simulated sufficiently accurately, an incorrect simulation cannot be prevented. The incorrect simulation includes the case where information of part of the object that is hidden and cannot be seen based on the posture of the digital mannequin and position of the object is presented to the designer of the operation, and the designer designs and specifies the action of the digital mannequin based on the information.
In the method described in (7) above, although perception and activities of an operator are attempted to be simulated, specific technology to achieve the goal is not disclosed. That is, the method discloses no details of the data and information processing algorithm to simulate the perception and activities. The method only implies the target items to be analyzed. Furthermore, according to this method, the ease of usability of the operation object is evaluated by determining whether or not a workload calculated by the simulation exceeds a threshold value. However, the method does not determine which factor among the ones influencing the operating state is responsible for the increased workload and does not determine to what extent that factor is responsible for the increased workload. Therefore, although the usability of the entire operation object can be determined, it is difficult to determine which part of the operation object must be modified.
In this method, if an operational error occurs in the simulation, the occurrence is only reported. However, an actual human behavior is capable of learning effective operations and reminders of the operations based on an operation history including operational errors. Accordingly, to execute a more realistic simulation, the method should include modification means for modifying the control of the operator actions depending on the operational errors by using feedback. However, this method does not provide specific modification means, which is a problem.
As described above, all the known methods do not disclose specific technologies that allow for automatic design of the human interface. Therefore, although systems having a variety of operations require a large number of human interface elements, the layout design of the control panel of the system is carried out by hand, thus disadvantageously imposing an enormous burden on the designers.